please could you check the first 2 then explain the method on the other 2

Question

1)5.2x10^6 + 3x10^5
5200000+300000=5500000
5.5x10^6

2)4.2x10^5 + 1.28x10^6
420000+1280000=1700000
1.7x10^6

method please

3)6.5x10^-3 - 3.5x10^-9
0.065-0.000000035=0.064999965
how do you convert this number into standard form?

4)400/(5x10^6)
i don't get how to work this one out

please could you help/explain. thanks.

Answer 1

You did 3) wrong. Using your method..
3)6.5x10^-3 - 3.5x10^-9
0.006 5-0.000 000 003 5=0.0059999965
5.9999965 x 10^-3

Let me show you an easier way. Convert both numbers to the same power.

6.5E-3 - 3.5E-9
6.5E-3 - 3.5E-3E-6
(6.5- .000 0035 )E-3
6.499 99965 E-3

another example
5.2x10^6 + 3x10^5
52.0E5+3E5
55E5 or 5.5E6

Lastly
4)400/(5x10^6)
4E2/5E6= .8E(2-6)=.8E-4=8E-5

Answer 2

what does E stand for?

Answer 3

E means x 10^ It is often used in computers, calculators, and in ASCII chat as here. It is easier.